It's common for a president to issue a flurry of last-minute rules before stepping down, particularly when a successor is from a different party. And as the Washington Post notes: Starting with Ronald Reagan, it has become a tradition for a president on his first day in office to issue a directive that voids the ones that have not yet gone into effect.

The Jan. 20 memo from Rahm Emanuel, President Obama's chief of staff, said: “It is important that President Obama’s appointees and designees have the opportunity to review and approve any new or pending regulations.” Therefore, "no proposed or final regulation should be sent to the Office of Federal Register for publication unless and until it has been reviewed and approved by a department or agency head appointed or designated by the President after noon on January 20, 2009, or in the case of the Department of Defense, the Secretary of Defense."

President Obama's order successfully blocked several of the Bush administration's late-term rules, but many went into effect before he took office, meaning that reversing them will probably take years. The nonprofit investigative journalism shop ProPublica has been tracking new rules from the Bush administration over the past two months. Of the 65 rules they list, 23 went into effect before Obama's inaguration; one-third of those new rules went into force fewer than three days before Obama took office.

Probably the most significant of the environmental rules already in force is a change to the Endangered Species Act that eases requirements for federal agencies to consult with scientists at the Fish and Wildlife or National Marine Fisheries services about the effects of their actions on threatened species. Under the new rule, which took effect nine days before Obama’s inauguration, federal agencies can in many cases simply check with their own personnel to determine if their projects will harm any of the 1,247 animal and 747 plant species listed as endangered or threatened.

ProPublica's Joaquin Sapien notes that Obama has two options for reversing rules that are already in effect. He could try to replace the rules with new rules, a process that Mr. Sapien calls "enormously difficult" because it resets the rulemaking process and opens it to legal challenges.

Or he could ask Congress to invoke the little-known Congressional Review Act, which allows the legislative body to kill a rule within "60 legislative days" – about six months – after it goes into effect. That law, which was passed in 1996 by the GOP-controlled Congress in an attempt to halt what was seen as excessive regulation by President Clinton, has been used only once.